News

Renovations on dam continue

A project to modernize the aging dam at Two Buttes Reservoir is back on track after it was slowed by a rain event in April that flooded the work site.

Last winter, when Two Buttes was dry, heavy equipment operators built a temporary cofferdam and removed 17 feet of sediment to get to the head gates at the bottom of the dam. April 12-13, a localized rainstorm filled the work site with several thousand gallons of water.

"The cofferdam worked the way we hoped it would, but there was so much rain it overtopped the cofferdam and flooded our work site," said John Clark, an engineer with Colorado Parks and Wildlife. "Over the next few days, we hope to get the work site dried out so we can continue the process of determining what it will take to bring the old dam up to modern standards."

Draining the work site will not release the water in the reservoir because the cofferdam separates the reservoir from the work site. The water in the work site will be released slowly so some of it can be captured in the swimming pond downstream known as "The Black Hole".

The dam at Two Buttes is 104 years old. "Back in 1908 they built everything by hand and didn't leave many records behind, so we need a geotechnical engineering study to determine the extent of repairs necessary to modernize the structure," said Clark.

Repairs in 1925, 1951, 1953 and 1965 kept the structure standing, but heavy sediment deposits and years of rust have made one of the two head gates inoperable.

Advertisement

"After we get the work site dried out, our next step is contract a team of geotechnical experts to install piezometers and determine design parameters for the rehabilitation of the outlet works," Clark said. A piezometer is a device used to measure water pressure under an earthen embankment.

Eventually, a modern outlet tower will be constructed with new controls for the head gates.

Two Buttes Reservoir is entirely dependent on local rainwater to keep it full. Drought conditions caused it to dry up completely in 2009.

The work is being done because state engineers categorize the dam as hydraulically inadequate because the earthen structure is not up to modern dam design standards.

"The long-term goal is to get the hazardous designation lifted and bring the dam up to current safety levels," said Travis Black, Colorado Parks and Wildlife area manager from Lamar. Black said the road to the dam is closed, but the work will not affect recreation in the rest of the Two Buttes State Wildlife Area.

Engineers will not be able to determine a completion date for the project until the next phase of geotechnical investigation provides data that will indicate how much work will be required.